1. Field of the Invention
The invention relates to an Ni—Fe—Cr—Mo alloy, especially a modified alloy in accordance with EN Material No. 1.4562 as well as its use.
2. The Prior Art
The alloy with Material No. 1.4562 has on the average the following chemical composition (standard values in mass %) Ni 31%, Mn 1.7%, Cr 27%, Mo 6.5%, Cu 1.3%, N 0.2%.
DE 32 23 457 A1 relates to an alloy, especially for the manufacture of highly loadable pipework of deep boreholes or the like with elevated resistance to stress corrosion cracking, consisting of C≦0.1%, Mn 3-20%, S≦0.005%, Al≦0.5%, Cr 22.5-35%, W 0-8%, Si≦1%, P≦0.03%, N 0-0.3%, Ni 25-60%, Mo 0-4%, Cu 0-2%, RE 0-0.1%, Mg 0-0.1%, Ca 0-0.1%, Co 0-2%, Y 0-0.2%, Ti 0-0.5%, whereinCr (%)+10Mo (%)+5W (%)≧50%½Mn (%)+Ni (%)≧35(%)1.5%≦Mo (%)+½W (%)<4.
From U.S. Pat. No. 5,841,046, a high-strength corrosion-resistant austenitic non-rusting steel, which contains an effect total (PREN)>55, can be inferred. An alloy of the following composition (in mass %) is presented: max. 0.08% C, 0.5-12.5% Mn, 20-29% Cr, 17-35% Ni, 3-10% Mo, >0.7% N, up to 1.0% Si, up to 0.02% B, up to 0.02% Mg, up to 0.05% Ce, remainder iron. For chromium contents between 24 and 28%, the nickel contents are indicated as between 21 and 23%, wherein the effect total (PREN) ranges between 49 and 65. In this state of the art, the extremely high nitrogen content is of significance.
In U.S. Pat. No. 4,824,638, a corrosion-resistant alloy of the following chemical composition (in mass %) is described: 20.5-32% nickel, 23.5 to 27.5% chromium, 4 to 6.7% molybdenum, 0.7 to 3.6% copper, up to 0.09% carbon, up to 1.5% silicon, up to 5% cobalt, up to 0.45% nitrogen, up to 1% titanium, up to 0.8% niobium, up to 0.3% rare earths (Ce, La, mixed metal), up to 2% manganese, up to 1.6% tantalum, remainder iron, wherein the sum of the nickel and cobalt contents is between 25.5 and 32% and the chromium content is exceeded by 2 to 6.2%.
From EP 0 292 061 A1, an alloy has become known with (in mass %) 30-32Ni, 26-28Cr, 0.5-1.5% Cu, max. 2% Mn, max. 1% Si, max. 0.2% Al, max. 0.02% C, remainder Fe, including unavoidable admixtures, which furthermore also contain 6-7% Mo and 0.1-0.25% N.
The alloy in accordance with EP 0 292 061 A1 was developed in order to be able to make available a material that is suitable for the manufacture of structural parts that must have a good corrosion resistance, especially to pitting corrosion and/or stress corrosion cracking, in aqueous, neutral or acid media with high chloride ion concentration. It is also intended to be usable for the manufacture of structural parts that must have an erosion rate of less than 0.20 mm/year in technical phosphoric acid with a chloride ion concentration up to 1000 ppm at 100° C. At the same time, it should be suitable for the manufacture of structural parts that must have a pitting corrosion potential of at least 1000 mVH at 75° C. and of at least 800 mVH at 90° C. in aqueous neutral media with a chloride ion concentration on the order of magnitude of 20,000 ppm. It should further be suitable as material for the manufacture of structural parts that must have a critical pitting corrosion temperature of at least 80° C. and a critical stress corrosion cracking temperature of at least 50° C. in acid media with a chloride ion concentration of 50,000 ppm and higher, such as, e.g. in an FeCl3 solution.
Consequently, this alloy used heretofore has in practice more than satisfied the expectations placed on it. However, the very high solution annealing temperature for dissolution of the brittle sigma phase, which according to VdTÜV Material Sheet 509/1, December 2009 version, must lie at 1150 to 1180° C., together with the additional criterion of a subsequent rapid cooling by means of quenching in water or by means of compressed air (depending on the wall thickness), in such a way that the temperature range down to 650° C. is rapidly transited, has been found to be disadvantageous for this alloy. For the assurance of a flawless dissolution of the sigma phase even for thicker-walled structural parts, at least the upper temperature of 1180° C. must be used in the industrial practice. Cases are now known in which such a solution annealing treatment must be integrated into the manufacturing process, for example in the hot cladding of large sheet sizes in the sandwich package or in the hot pressing of thick-walled vessel bottoms. In this connection, it has been found that the solution annealing and cooling conditions mentioned in the foregoing then cannot be satisfied to the extent that the high pitting corrosion and stress corrosion cracking temperatures expected for this alloy are now not attained because of the separation of sigma phase.
For alloys (UNS 32654/654 SMO) with similar contents of chromium 24-26% and molybdenum 7-8%, the following empirical formula for the dependence of the sigma solvus temperature on the alloying components is found in the literature (Rechsteiner ETH Zurich Publ. No.: 10647):T sigma-solvus=24.6Cr+6.7Mn+50.9Mo+92.2Si−9.2Ni−17.9Cu−230.4C−238.4N+447 (element units: mass percent).
Accordingly, the elements chromium, molybdenum, silicon and manganese raise the sigma solvus temperature; the elements nickel, copper and especially nitrogen act to lower the sigma solvus temperature.